CODEWITHSUNDEEP
javalambdajava-8java-stream
lapkritinis
lapkritinis

Reputation: 2814

Lambda expressions and nested arrays

I'm trying to come up with some nice lambda expressions to build "desiredResult" from "customers" ArrayList. I implemented it in an old ugly way "for" loop. I know there should be nice one-liners, but I can't think of any method - nested arrays come into my way.

Iterable<List<?>> params;
Customer customer1 = new Customer("John", "Nowhere");
Customer customer2 = new Customer("Alma", "Somewhere");
Customer customer3 = new Customer("Nemo", "Here");
Collection<Customer> customers = new ArrayList<>();
customers.add(customer1);
customers.add(customer2);
customers.add(customer3);

Collection<List<?>> desiredResult = new ArrayList<>();
for (Customer customer : customers) {
    List<Object> list = new ArrayList<>();
    list.add(customer.getName());
    list.add(customer.getAddress());
    list.add("VIP");
    desiredResult.add(list);
}
params = desiredResult;

Upvotes: 4

Views: 440

Answers (2)

Mureinik
Mureinik

Reputation: 311088

I'd just use Arrays.asList for creating the inner lists, which makes the problem much simpler:

Collection<List<?>> desiredResult = 
    customers.stream()
             .map(c -> Arrays.asList(c.getName(), c.getAddress(), "VIP"))
             .collect(Collectors.toList());

If you absolutely must have an ArrayList, just wrap the Arrays.asList call with it.

Upvotes: 4

assylias
assylias

Reputation: 328598

Here is a suggestion:

Collection<List<?>> desiredResult = customers.stream()
         .map(MyClass::customerToList)
         .collect(toList());

I have extracted the list building into a separate method for better readability - the corresponding method would look like this:

private static List<Object> customerToList(Customer c) {
  List<Object> list = new ArrayList<>();
  list.add(c.getName());
  list.add(c.getAddress());
  list.add("VIP");      
  return list;
}

Upvotes: 3

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